U.S. patent application number 15/250057 was filed with the patent office on 2018-03-01 for methods for directionally recrystallizing additively-manufactured metallic articles by heat treatment with a gradient furnace.
This patent application is currently assigned to HONEYWELL INTERNATIONAL INC.. The applicant listed for this patent is HONEYWELL INTERNATIONAL INC.. Invention is credited to Brian G. Baughman, James J. Cobb, Donald G. Godfrey, Mamballykalathil Menon, Mark C. Morris.
Application Number | 20180056396 15/250057 |
Document ID | / |
Family ID | 59699475 |
Filed Date | 2018-03-01 |
United States Patent
Application |
20180056396 |
Kind Code |
A1 |
Menon; Mamballykalathil ; et
al. |
March 1, 2018 |
METHODS FOR DIRECTIONALLY RECRYSTALLIZING ADDITIVELY-MANUFACTURED
METALLIC ARTICLES BY HEAT TREATMENT WITH A GRADIENT FURNACE
Abstract
A method for manufacturing a metallic article includes providing
or obtaining a metallic material in powder form, using an additive
manufacturing process, building the metallic article from the
powder-form metallic material, layer-by-layer, in a build
direction, wherein as a result of the additive manufacturing
process, the metallic article comprises columnar grain structures
oriented in the build direction, and conveying the metallic article
through a gradient furnace in a direction of conveyance from a
first area of the gradient furnace to a second area of the gradient
furnace to increase a size of the columnar grain structures in the
metallic article. The metallic article is conveyed through the
gradient furnace in an orientation such that the columnar
structures oriented in the build direction are substantially
parallel to the direction of conveyance.
Inventors: |
Menon; Mamballykalathil;
(Gilbert, AZ) ; Baughman; Brian G.; (Surprise,
AZ) ; Cobb; James J.; (Casa Grande, AZ) ;
Godfrey; Donald G.; (Phoenix, AZ) ; Morris; Mark
C.; (Phoenix, AZ) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
HONEYWELL INTERNATIONAL INC. |
Morris Plains |
NJ |
US |
|
|
Assignee: |
HONEYWELL INTERNATIONAL
INC.
Morris Plains
NJ
|
Family ID: |
59699475 |
Appl. No.: |
15/250057 |
Filed: |
August 29, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B22F 5/009 20130101;
B22F 2003/247 20130101; B22F 3/15 20130101; F01D 5/147 20130101;
F01D 5/12 20130101; B23K 2101/001 20180801; B23K 2103/08 20180801;
Y02P 10/25 20151101; B22F 5/04 20130101; B22F 3/1055 20130101; B22F
2301/15 20130101; B22F 2003/1058 20130101; B33Y 10/00 20141201;
B23K 15/0086 20130101; B22F 2003/248 20130101; B33Y 80/00 20141201;
B22F 2998/10 20130101; F05D 2230/22 20130101; B33Y 40/00 20141201;
C22F 1/10 20130101; B22F 3/24 20130101; B22F 2998/10 20130101; B22F
3/1055 20130101; B22F 2003/248 20130101; B22F 2003/247 20130101;
B22F 3/15 20130101 |
International
Class: |
B22F 3/24 20060101
B22F003/24; B22F 3/105 20060101 B22F003/105; B23K 15/00 20060101
B23K015/00; B22F 5/00 20060101 B22F005/00; B22F 5/04 20060101
B22F005/04; B22F 3/15 20060101 B22F003/15; B33Y 10/00 20060101
B33Y010/00; B33Y 40/00 20060101 B33Y040/00; B33Y 80/00 20060101
B33Y080/00; C22F 1/10 20060101 C22F001/10 |
Claims
1. A method for manufacturing a metallic article comprising the
steps of: providing or obtaining a metallic material in powder
form; using an additive manufacturing process, building the
metallic article from the powder-form metallic material,
layer-by-layer, in a build direction, wherein as a result of the
additive manufacturing process, the metallic article comprises
columnar grain structures oriented in the build direction; building
a sacrificial piece onto the metallic article using the additive
manufacturing process, the sacrificial piece being metallurgically
coupled to the metallic article and comprising the metallic
material; and conveying the metallic article through a gradient
furnace in a direction of conveyance from a first area of the
gradient furnace to a second area of the gradient furnace to
increase a size of the columnar grain structures in the metallic
article, wherein the metallic article is conveyed through the
gradient furnace in an orientation such that the columnar
structures oriented in the build direction are substantially
parallel to the direction of conveyance, wherein the first area of
the gradient furnace heats the metallic article to a temperature
that is below a solvus temperature of the metallic material and the
second area of the gradient furnace heats the metallic article to a
temperature that is above the solvus temperature of the metallic
material, the temperature of the gradient furnace increasing in a
gradated manner from the first area to the second area, and wherein
the metallic article is oriented with respect to the gradient
furnace such that the sacrificial piece enters the gradient furnace
subsequent to the metallic article onto which the sacrificial piece
is built.
2. The method of claim 1, wherein the additive manufacturing
processes is either electron beam melting (EBM) or direct metal
laser fusion (DMLF).
3. The method of claim 1, further comprising removing the
sacrificial piece from the metallic article subsequent to the step
of conveying the metallic article through the gradient furnace.
4. The method of claim 1, wherein the additive manufacturing
process employs a heated build plate to maintain the metallic
article at an elevated temperature as it is built, layer-by-layer,
in the build direction.
5. The method of claim 1, wherein the additive manufacturing
process employs a directionally-crystallized metallic seed layer
and builds the metallic article, layer-by-layer, from the seed
layer, thereby resulting in an improved columnar grain structure,
oriented in the build direction, of the metallic article.
6. The method of claim 1, wherein the metallic material comprises a
Ni-based superalloy.
7. The method of claim 1, wherein the metallic article comprises a
gas turbine engine component, such as a turbine blade, vane, or
nozzle.
8. The method of claim 1, further comprising, subsequent to
conveying the metallic article through the gradient furnace,
quenching the metallic article in a non-oil quenching medium.
9. The method of claim 8, further comprising, subsequent to
quenching the metallic article, performing one or more of
hot-isostatic pressing, ageing, and machining of the metallic
article.
10. The method of claim 1, wherein the step of conveying the
metallic article through the gradient furnace is performed at a
conveyance rate of about 1 to about 2 inches per hour.
Description
TECHNICAL FIELD
[0001] The present disclosure generally relates to metallic article
manufacturing methods. More particularly, the present disclosure
relates to the formation of a directionally recrystallized
microstructure in additively-manufactured metallic articles using a
gradient furnace.
BACKGROUND
[0002] Gas turbine engines may be used to power various types of
vehicles and systems, such as air or land-based vehicles. In
typical gas turbine engines, compressed air generated by axial
and/or radial compressors is mixed with fuel and burned, and the
expanding hot combustion gases are directed along a flowpath and
through a turbine nozzle having stationary vanes. The combustion
gas flow deflects off of the vanes and impinges upon turbine blades
of a turbine rotor. A rotatable turbine disk or wheel, from which
the turbine blades extend, spins at high speeds to produce power.
Gas turbine engines used in aircraft use the power to draw more air
into the engine and to pass high velocity combustion gas out of the
gas turbine aft end to produce a forward thrust.
[0003] In the development and testing of new designs for gas
turbine engine components, it is important to minimize the amount
of time required to manufacture "critical path components," like
cooled turbine blades and vanes. In high performance gas turbine
engine applications, these cooled turbine blades and vanes are
typically manufactured using superalloy materials and casting
processes to produce a single crystal or polycrystalline material.
For example, cast turbine blades and vanes can be made by means of
directional solidification of a liquid melt pool that is in the
shape of the article. The melted alloy in the shape of the article
is then slowly solidified from one end by a process that extracts
heat in the direction in which the fast growing grains are desired
to be oriented in its preferred growth direction. The growth of
these fast growing grains naturally occurs in the crystallographic
direction with the miller indices of <001>.
[0004] However, for the above-noted purposes of development and
testing, the casting process takes an undesirably long time and
involves (i) making core dies, cores, wax dies, wax patterns, and
ceramic molds with an inner cavity in the form of the article, (ii)
a melt furnace of sufficient inner volume in which the alloy can be
completely melted, (iii) a ceramic sieve to filter out unwanted
ingredients in the melt pool, and (iv) a heated furnace with heat
extraction capabilities. As such, it should be appreciated that the
investment for this assembly of equipment is large, and the lead
time to make the first article takes many months. This prior art
casting process is too expensive and too time consuming for
fast-paced and/or low volume development programs.
[0005] Hence, there is a need for manufacturing methods that allow
for the production of metallic articles, such as gas turbine engine
components, which exhibit properties that are the same as or
similar to traditionally-cast directionally-solidified articles,
yet which do not require the time and expense of traditional
casting processes. Furthermore, other desirable features and
characteristics of directionally recrystallized microstructure in
additively-manufactured metallic articles, and the method for
manufacturing the same will become apparent from the subsequent
detailed description and the appended claims, taken in conjunction
with the accompanying drawings and the preceding background.
BRIEF SUMMARY
[0006] Various methods for manufacturing metallic articles are
disclosed herein. In one exemplary embodiment, a method for
manufacturing a metallic article includes the steps of providing or
obtaining a metallic material in powder form, using an additive
manufacturing process, building the metallic article from the
powder-form metallic material, layer-by-layer, in a build
direction, wherein as a result of the additive manufacturing
process, the metallic article comprises columnar grain structures
oriented in the build direction, and conveying the metallic article
through a gradient furnace in a direction of conveyance from a
first area of the gradient furnace to a second area of the gradient
furnace to increase the length of the columnar grain structure in
the metallic article. The metallic article is conveyed through the
gradient furnace in an orientation such that the columnar
structures oriented in the build direction are substantially
parallel to the direction of conveyance.
[0007] In another exemplary embodiment, A method for manufacturing
a metallic article includes the steps of providing or obtaining a
metallic material in powder form, using an additive manufacturing
process, building the metallic article from the powder-form
metallic material, layer-by-layer, in a build direction, wherein as
a result of the additive manufacturing process, the metallic
article comprises columnar grain structures oriented in the build
direction, and building a sacrificial piece onto the metallic
article using the additive manufacturing process, the sacrificial
piece being metallurgically coupled to the metallic article and
comprising the metallic material. The method further includes
conveying the metallic article through a gradient furnace in a
direction of conveyance from a first area of the gradient furnace
to a second area of the gradient furnace to increase a size of the
columnar grain structures in the metallic article. The metallic
article is conveyed through the gradient furnace in an orientation
such that the columnar structures oriented in the build direction
are substantially parallel to the direction of conveyance. The
first area of the gradient furnace heats the metallic article to a
temperature that is below a solvus temperature of the metallic
material and the second area of the gradient furnace heats the
metallic article to a temperature that is above the solvus
temperature of the metallic material, the temperature of the
gradient furnace increasing in a gradated manner from the first
area to the second area. Furthermore, the metallic article is
oriented with respect to the gradient furnace such that the
sacrificial piece enters the gradient furnace subsequent to the
metallic article onto which the sacrificial piece is built.
[0008] This summary is provided to describe select concepts in a
simplified form that are further described in the Detailed
Description. This summary is not intended to identify key or
essential features of the claimed subject matter, nor is it
intended to be used as an aid in determining the scope of the
claimed subject matter.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] The present invention will hereinafter be described in
conjunction with the following drawing figures, wherein like
numerals denote like elements, and wherein:
[0010] FIG. 1 is an exemplary gas turbine engine component,
particularly a turbine blade, which may serve as the metallic
article of the present disclosure, in some embodiments;
[0011] FIG. 2 is a flow diagram illustrating steps in a method of
forming a metallic article using additive manufacturing techniques
in accordance with some embodiments the present disclosure;
[0012] FIG. 3 is an exemplary additive manufacturing system
suitable for use in forming a metallic article in accordance with
some embodiments of the present disclosure;
[0013] FIG. 4 illustrates the inclusion of a sacrificial heat sink
on an article in accordance with some embodiments of the present
disclosure; and
[0014] FIG. 5 illustrates an exemplary gradient furnace, and the
processing of an article in the exemplary gradient furnace, in
accordance with some embodiments of the present disclosure.
DETAILED DESCRIPTION
[0015] The following detailed description is merely exemplary in
nature and is not intended to limit the invention or the
application and uses of the invention. As used herein, the word
"exemplary" means "serving as an example, instance, or
illustration." Thus, any embodiment described herein as "exemplary"
is not necessarily to be construed as preferred or advantageous
over other embodiments. All of the embodiments described herein are
exemplary embodiments provided to enable persons skilled in the art
to make or use the invention and not to limit the scope of the
invention which is defined by the claims. Furthermore, there is no
intention to be bound by any expressed or implied theory presented
in the preceding technical field, background, brief summary, or the
following detailed description.
[0016] The present disclosure provides methods for
directionally-recrystallizing metallic articles, such as gas
turbine engine blades and vanes, which are manufactured using
additive manufacturing techniques, such as direct metal laser
sintering or electron beam melting. Although the present disclosure
is provided in the context of gas turbine engine development and
testing, it should be appreciated that the methods described herein
may be used for the manufacturing of any metallic article to be
used for any application. The disclosed methods produced
directionally-recrystallized metallic articles that exhibit
metallic properties that are the same as or similar to
traditionally-cast directionally-solidified articles. Beneficially,
the disclosed methods allow for the rapid design and production of
such components to reduce cycle time in the development and testing
of critical path components. Moreover, design and testing of the
articles improved due to the fact that the metallic articles
manufactured in accordance with the present disclosure, due to
their enhanced crystallographic orientation (as compared
non-resolidified additively-manufactured articles), are able to be
tested at higher operating temperatures and for longer periods of
time.
[0017] FIG. 1 illustrates an exemplary gas turbine engine blade
configuration 100 that may be suitable for use in connection with
the methods described herein, in one embodiment. The blade 100
includes a blade attachment section 102, an airfoil 104, and a
platform 106. The blade attachment section 102 provides an area in
which a shape is machined. In an embodiment, the shape corresponds
with a shape formed in a respective blade attachment slot (not
shown) of the turbine hub. For example, in some embodiments, the
shape may be what is commonly referred to in the art as a "firtree"
shape. In other embodiments, the shape may be a beveled shape.
However, in other embodiments, any one of numerous other shapes
suitable for attaching the blade 100 to the turbine may be
alternatively machined therein.
[0018] The airfoil 104 has a root 108 and two outer walls 110, 112.
The root 108 is attached to the platform 106 and each outer wall
110, 112 has outer surfaces that define an airfoil shape. The
airfoil shape includes a leading edge 114, a trailing edge 116, a
pressure side 118 along the first outer wall 110, a suction side
120 along the second outer wall 112, a tip outer wall 122, a
plurality of pressure side discharge trailing edge slots 124 (the
edge slot at the tip is the tip trailing edge slot 125), a tip
plenum 126 recessed radially inward from the tip outer wall 122,
and a series of film cooling holes 128. Holes 128 may be provided
along the leading edge 114, along the first outer wall 110 near the
tip outer wall 122, and/or along the tip plenum 126. Though not
shown in FIG. 1, the blade 100 may have an internal cooling circuit
formed therein, which may extend from an opening in the platform
106 through the blade 100 and may include various passages that
eventually communicate with the plurality of trailing edge slots
124 and the tip trailing edge slot 125, or other openings (not
shown) that may be formed in the blade 100. In particular, the
convex suction side wall 112, the concave pressure side wall 110,
and the tip 122 each include interior surfaces defining the
internal cooling circuit.
[0019] The gas turbine engine blade 100 of FIG. 1, or any other
metallic article (for use in a gas turbine engine or otherwise),
may be manufactured initially in accordance with the additive
manufacturing techniques described in connection with FIGS. 2 and
3. FIG. 2 is a flowchart illustrating a method 200 for
manufacturing an article/component, for example the gas turbine
engine blade 100, using additive manufacturing techniques based on
low energy density energy beams. In a first step 210, a model, such
as a design model, of the component may be defined in any suitable
manner. For example, the model may be designed with computer aided
design (CAD) software and may include three-dimensional ("3D")
numeric coordinates of the entire configuration of the component
including both external and internal surfaces. In one exemplary
embodiment, the model may include a number of successive
two-dimensional ("2D") cross-sectional slices that together form
the 3D component. Of course, it is not necessary that a "near-net"
component be formed using this process. Rather, it may simply be
desired to produce a "block" of the alloy using additive
manufacturing. Accordingly, the present disclosure should not be
considered as limited by any particular article/component
design.
[0020] In step 220 of the method 200, the component is formed
according to the model of step 210. In one exemplary embodiment, a
portion of the component is formed using a rapid prototyping or
additive layer manufacturing process. In other embodiments, the
entire component is formed using a rapid prototyping or additive
layer manufacturing process. Although additive layer manufacturing
processes are described in greater detail below, in still other
alternative embodiments, portions of the component may be forged or
cast in step 220.
[0021] Some examples of additive layer manufacturing processes
include: selective laser sintering in which a laser is used to
sinter a powder media in precisely controlled locations; laser wire
deposition in which a wire feedstock is melted by a laser and then
deposited and solidified in precise locations to build the product;
electron beam melting; laser engineered net shaping; and direct
metal deposition. In general, additive manufacturing techniques
provide flexibility in free-form fabrication without geometric
constraints, fast material processing time, and innovative joining
techniques. In one particular exemplary embodiment, direct metal
laser fusion (DMLF) is used to produce the article/component in
step 220, such as blade 100. DMLF is a commercially available
laser-based rapid prototyping and tooling process by which complex
parts may be directly produced by precision melting and
solidification of metal powder into successive layers of larger
structures, each layer corresponding to a cross-sectional layer of
the 3D component.
[0022] As such, in one exemplary embodiment, step 220 is performed
with DMLF techniques to form the component. However, prior to a
discussion of the subsequent method steps, reference is made to
FIG. 3, which is a schematic view of a DMLF system 300 for
manufacturing the component, for example one or more gas turbine
engine components, in accordance with an exemplary embodiment.
[0023] Referring to FIG. 3, the system 300 includes a fabrication
device 310, a powder delivery device 330, a scanner 342, and a low
energy density energy beam generator, such as a laser 360 (or an
electron beam generator) that functions to manufacture the article
350 (e.g., the component) with build material 370. The fabrication
device 310 includes a build container 312 with a fabrication
support 314 on which the article 350 is formed and supported. The
fabrication support 314 is movable within the build container 312
in a vertical direction and is adjusted in such a way to define a
working plane 316. The delivery device 330 includes a powder
chamber 332 with a delivery support 334 that supports the build
material 370 and is also movable in the vertical direction. The
delivery device 330 further includes a roller or wiper 336 that
transfers build material 370 from the delivery device 330 to the
fabrication device 310.
[0024] During operation, a build plate 340 may be installed on the
fabrication support 314. The fabrication support 314 is lowered and
the delivery support 334 is raised. The roller or wiper 336 scrapes
or otherwise pushes a portion of the build material 370 from the
delivery device 330 to form the working plane 316 in the
fabrication device 310. The laser 360 emits a laser beam 362, which
is directed by the scanner 342 onto the build material 370 in the
working plane 316 to selectively fuse the build material 370 into a
cross-sectional layer of the article 350 according to the design.
More specifically, the speed, position, and other operating
parameters of the laser beam 362 are controlled to selectively fuse
the powder of the build material 370 into larger structures by
rapidly melting the powder particles that may melt or diffuse into
the solid structure below, and subsequently, cool and re-solidify.
As such, based on the control of the laser beam 362, each layer of
build material 370 may include unfused and fused build material 370
that respectively corresponds to the cross-sectional passages and
walls that form the article 350. In general, the laser beam 362 is
relatively low power to selectively fuse the individual layer of
build material 370. As an example, the laser beam 362 may have a
power of approximately 50 to 500 Watts, although any suitable power
may be provided.
[0025] One aspect of the present disclosure is that the article 350
is fabricated with the build direction as the vertical/longitudinal
direction for the direction of desired elongated grains. Referring
back to FIG. 1, for example, the blade 100 would thus be
additively-manufactured starting from the bottom of the attachment
section 102, proceeding, layer-by-layer, up to the platform 106,
and thereafter proceeding to the airfoil 104, and finishing with
the tip outer wall 122. For other articles that are not blades, the
person having ordinary skill in the art will be well-aware of the
desired direction of elongated grains (which may be dependent on
the intended use of the article), and will utilize an
appropriately-oriented CAD schematic to achieve the layer-by-layer
additive manufacturing of the desired article accordingly.
[0026] In some embodiments, optionally, a directionally solidified
or single crystal seed starter may be fastened to the build plate
340 to promote directionally solidified grains in the desired
vertical/longitudinal direction. In an embodiment, a seed crystal
is provided having at least a predetermined primary orientation.
For example, seed crystals employed for producing a directionally
solidified and single crystal microstructures may have at least the
predetermined primary orientation. Scanning the pattern to melt the
deposited powder allows the deposited metal powder to acquire the
crystallographic orientation of the seed crystal. Accordingly, the
initial layer comprises a plurality of grains that are arranged in
crystal structures having the predetermined primary orientation.
The desired primary orientation is obtained by positioning the seed
crystal in the predetermined primary orientation. In an embodiment,
the predetermined primary orientation is <001>. Because the
initial layer has substantially the same crystallographic
microstructure as the seed crystal, for these applications the
successive layer comprises a plurality of grains that are arranged
in crystal structures having at least the predetermined primary
orientation. Further information regarding the use of seed crystals
may be found in commonly-assigned U.S. Pat. No. 8,728,388, the
contents of which are herein incorporated by reference in their
entirety. In some optional embodiments, the build plate 340 may be
heated during the build process in order to support continued
growth in the primary orientation.
[0027] Upon completion of a respective layer, the fabrication
support 314 is lowered and the delivery support 334 is raised.
Typically, the fabrication support 314, and thus the article 350,
does not move in a horizontal plane during this step. The roller or
wiper 336 again pushes a portion of the build material 370 from the
delivery device 330 to form an additional layer of build material
370 on the working plane 316 of the fabrication device 310. The
laser beam 362 is movably supported relative to the article 350 and
is again controlled to selectively form another cross-sectional
layer. As such, the article 350 is positioned in a bed of build
material 370 as the successive layers are formed such that the
unfused and fused material supports subsequent layers. This process
is continued according to the modeled design as successive
cross-sectional layers are formed into the completed desired
portion, e.g., the component of step 220.
[0028] The delivery of build material 370 and movement of the
article 350 in the vertical direction are relatively constant and
only the movement of the laser beam 362 is selectively controlled
to provide a simpler and more precise implementation. The localized
fusing of the build material 370 enables more precise placement of
fused material to reduce or eliminate the occurrence of
over-deposition of material and excessive energy or heat, which may
otherwise result in cracking or distortion. The unused and unfused
build material 370 may be reused, thereby further reducing
scrap.
[0029] Any suitable laser and laser parameters may be used,
including considerations with respect to power, laser beam spot
size, and scanning velocity. The build material 370 may be provided
as a metallic superalloy. For use in gas turbine engines,
nickel-based superalloys are commonly used. One example of a
suitable nickel-based superalloy for use with the methods of the
present disclosure is the alloy Mar-M-247, the elemental
constituents of which are well-known in the art.
[0030] Returning to FIG. 2, at the completion of step 220, the
article/component may be given a stress relief treatment and then
is removed from the additive manufacturing system (e.g., from the
DMLF system 300). In optional step 230, the component formed in
step 220 may undergo finishing treatments. Finishing treatments may
include, for example, polishing and/or the application of coatings.
If necessary, the component may be machined to final
specifications. For example, in some embodiments in accordance with
the present disclosure, gas turbine engine components can be
manufactured by the DMLF process (optionally including machining)
described herein.
[0031] In some embodiments of the present disclosure, optionally, a
sacrificial gradient heat sink portion 401 is fabricated outside
the article, e.g., blade 100, and metallurgically coupled with the
article 100, starting from the build plate 340, as shown in FIG. 4.
The sacrificial gradient heat sink may be provided to ensure a
thermal gradient is present in the component during subsequent heat
treatment, as will be described in greater detail below. In some
embodiments, the sacrificial gradient heat sink portion may be
fabricated on the opposite side of the component 100 away from the
build plate 340. The sacrificial gradient heat sink portion 401 may
be provided to extract heat out of the component during subsequent
heat treatment, thus maintaining the thermal gradient necessary to
directionally recrystallize the microstructure in the preferential
(longitudinal) direction.
[0032] Unlike prior art methods producing nickel based superalloy
parts, the present disclosure utilizes an innovative gradient
anneal heat treatment to produce a directionally recrystallized
microstructure in additively-manufactured articles to give an added
directional force for secondary recrystallization in a preferred
direction. Un-treated additively-manufactured articles consist of
epitaxially-grown fine grains at each section, generally
perpendicular to the build direction. In this disclosure, an added
thermal force is applied for further grain growth to occur in the
build direction. As such, the present disclosure utilizes the
elongated grain growth from the additive manufacturing process to
obtain a directionally recrystallized microstructure for improved
mechanical properties such as creep or stress rupture strength.
Combining an additively-manufactured elongated grain microstructure
in conjunction with an innovative gradient heat treatment method
produces a directionally recrystallized microstructure that
provides superior mechanical properties over using
additively-manufactured parts without a gradient heat
treatment.
[0033] Referring now to FIG. 5, the article (e.g., blade 100)
(including sacrificial heat sink 401 if provided) are processed in
a gradient furnace 500, where the thermal gradient in the article
during the heat treatment is aligned with the desired elongated
grain orientation for the article. The gradient furnace generally
includes a furnace inlet 511 and a furnace outlet 512, and a
conveyor belt 501 that between the inlet 511 and the outlet 512.
Regions of the interior of furnace 500 nearer the furnace inlet 511
may be referred to as a cooler temperature region 521, whereas
regions of the interior of furnace 500 nearer the furnace outlet
512 may be referred to as a hotter temperature region 522. The
cooler temperature region 521 operates at a temperature below the
gamma prime solvus temperature of the metal material (e.g.,
nickel-based superalloy) that forms the article, whereas the hotter
temperature region 522 operates at a temperature above the gamma
prime solvus temperature of the metal material. A temperature
gradient exists between the regions 521 and 522, as illustrated in
FIG. 5.
[0034] The component is processed through the gradient furnace 500
such that the sacrificial heat sink 401 (if provided) is the last
portion of the component to be heated by the furnace 500. The
sacrificial heat sink 401 (while still in the furnace cool zone)
draws heat from the article which is in the hotter zones of the
furnace (522), thus providing a temperature gradient in the
additively-manufactured article, which then results in a
directionally recrystallized microstructure. The article is
processed through the gradient furnace 500 with the temperature of
the article continuing to ramp until it is above its gamma prime
solvus temperature. In some embodiments, as illustrated, the
article temperature ramps up past the gamma prime solvus
temperature while the sacrificial heat sink 401 (if provided) is
still in the lower temperature sub-solvus temperature zone of the
furnace 500.
[0035] The article is processed at a translational rate through the
furnace 500 until the entire article traverses through the high
temperature super-solvus temperature zone 522 to achieve
directionally recrystallized grain growth in the longitudinal
(oven-traverse) direction. In some embodiments, the step of
conveying the metallic article through the gradient furnace 500 is
performed at a conveyance rate of about 1 to about 2 inches per
hour, such as about 1.5 inches per hour. However, the actual rate
employed is dependent on the size, shape, and configuration of the
article, as well as the material employed, and may require as small
amount of experimentation by the operator to determine an optimal
rate for the article at issue.
[0036] Upon exiting the gradient furnace 500, the article has a
directionally-recrystallized microstructure, as alluded to above.
Subsequent to exiting the gradient furnace 500, further processing
steps may optionally be employed. These further processing steps
include, for example, quenching in a non-oil quenching medium,
removing the sacrificial heat sink portion 401 from the article,
ageing to optimize the mechanical properties of the article,
inspections to confirm acceptable metallography, machining to the
final, desired shape of the article, and encapsulation, such as
encapsulation according to the process disclosed in
commonly-assigned U.S. Patent Application Publication 2011/0311389,
the contents of which are herein incorporated by reference in their
entirety.
[0037] Accordingly, the present disclosure has provided methods for
directionally-recrystallizing metallic articles, such as gas
turbine engine blades and vanes, which are manufactured using
additive manufacturing techniques, such as direct metal laser
sintering or electron beam melting. Although the present disclosure
is provided in the context of gas turbine engine development and
testing, it should be appreciated that the methods described herein
may be used for the manufacturing of any metallic article to be
used for any application. The disclosed methods produced
directionally-recrystallized metallic articles that exhibit
metallic properties that are the same as or similar to
traditionally-cast directionally-solidified articles. Beneficially,
the disclosed methods allow for the rapid design and production of
such components to reduce cycle time in the development and testing
of critical path components.
[0038] In this document, relational terms such as first and second,
and the like may be used solely to distinguish one entity or action
from another entity or action without necessarily requiring or
implying any actual such relationship or order between such
entities or actions. Numerical ordinals such as "first," "second,"
"third," etc. simply denote different singles of a plurality and do
not imply any order or sequence unless specifically defined by the
claim language. The sequence of the text in any of the claims does
not imply that process steps must be performed in a temporal or
logical order according to such sequence unless it is specifically
defined by the language of the claim. The process steps may be
interchanged in any order without departing from the scope of the
invention as long as such an interchange does not contradict the
claim language and is not logically nonsensical.
[0039] Furthermore, depending on the context, words such as
"connect" or "coupled to" used in describing a relationship between
different elements do not imply that a direct physical connection
must be made between these elements. For example, two elements may
be connected to each other physically, electronically, logically,
or in any other manner, through one or more additional
elements.
[0040] While at least one exemplary embodiment has been presented
in the foregoing detailed description of the invention, it should
be appreciated that a vast number of variations exist. It should
also be appreciated that the exemplary embodiment or exemplary
embodiments are only examples, and are not intended to limit the
scope, applicability, or configuration of the invention in any way.
Rather, the foregoing detailed description will provide those
skilled in the art with a convenient road map for implementing an
exemplary embodiment of the invention. It being understood that
various changes may be made in the function and arrangement of
elements described in an exemplary embodiment without departing
from the scope of the invention as set forth in the appended
claims.
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